Neisseria meningitidis is a major cause of bacterial meningitis. All meningococcal strains have either a class 2 or class 3 major outer membrane protein of approximately 35 to 40,000 Mr. These proteins are the meningococcal porins and carry the serotype determinants. They have been evaluated as vaccine constituents. Despite their common function, there is considerable antigenic diversity among the class 2 and 3 proteins. The purpose of the present studies is to determine the sequence of the class 3 protein and to compare it to the published sequence of the class 2 protein in an attempt to define the serotype specific regions. Furthermore, we are interested in cloning the class 2 and class 3 genes, and create chimeric proteins to confirm the non homologous regions between these proteins as the important antigenic determinants. Since synthesis of these foreign porins is lethal to E. coli, our strategy was to clone the class 2 and class 3 genes under the control of the T7 RNA polymerase promoter. The T7 promoter is not recognized by the E. coli polymerase therefore plasmids containing genes that express toxic proteins can be stabilized in E. coli. Expression will be attempted by infection with a bacteriophage that provides T7 RNA polymerase to the cell, or in vitro by using a transcription-translation system. At present we have been able to sequence part of a 600 bp fragment believed to be part of the class 3 gene. Also two PCR fragments containing the entire genes for the class 3 and class 2 proteins have been cloned. Further confirmation will obtain sequencing the plasmids containing the two genes.